Process of liquefying gases with low boiling-point.



G. HILDEBRANDT. PROCESS OF LIQUEFYIN G GASES WITH LOW BOILING'POIN-T.

APPLICATION HLED JUNEII. 19M. I

PatentedSept. 26

Hmeoou En STATES PATENT OFFICE.

GO'P'IHOLD HILDEBRANDT, OF SPANDAU-TIEFWERDER, NEAR BERLIN, GERMANY, ASSIGNOR TO AMERICAN INDUSTRIAL GAS COMPANY, OF NEW YORK, N. Y., A

CORPORATION OF NEW YORK.

PROCESS OF LIQUEFYING GASES WITH LOW BOILING-POINT.

Specification of Letters Patent.

Patented Sept. 26, 1916.

Original application filed January 9, 1911, Serial No. 601,614. Divided and this application filed June 11, 1914. Serial No. 844,525.

To all whom it may concern 30 it known that I, Go'r'rnoLn Himmmmxnir, engineer, citizen of Germany, sub: ject of the King of Prussia and Emperor of Germany, residing at Spandau-Tiefwerder 29*, near Berlin, in the Kingdom of Prussia and Empire of Germany, have invented new and useful Improvements in Processes of Liquefying Gases with Low Boiling-Point, of which the following is a specification.

The liquefaction of gases with a low boiling point has heretofore generally been affected only by the regenerative method indicated by Siemens in the year 1857 which consists in compressing, cooling and expanding these gases such for example as nitrogen, oxygen,. hyrogen, etc., and con ducting the cooled gases thus obtained in counter current to fresh compressed gases, thereby producing an interchange of heat, which ultimately results in the desired l1quefaction. In accordance with various systems this expansion has taken place either in a counter current system of pipes or in open cavities. This method has presented the defeet that the liquefying period occupies a considerable time as the greatest cooling which is theoretically possible cannot be reached owing to the apparatus employed, because with this method of expanding, the fractional resistances of the counter current system of piping do notpermit of fully utilizing the energy supplied in the compressed gases, and by this method it is impossible to utilize the kinetic energy of the gas molecules obtained by expanding to such an extent that their pressure falls below atmospheric pressure after the expansion.

It is well known that compressed gas when it issues through an aperture into a space of less pressure and escapes with an increased kinetic energy, is cooled close to the discharge aperture. This cooling (called by Travers velocity cooling) has not been used up to the present time for the liquefication or the separation of gas although it represents a very rich source of cold because this cooling exists only immediately after passing through the aperture and disappears at a relatively short distance from the aperture, the velocity of the stream of gas being reduced by friction caused by its impinging against the wall of the vessel into which it flows. Therefore in order to produce low temperatures cooling by utilizing the Joule- .lhompson eli'ect only was applied which is the result of the internal work only caused by the expanding gas.

I have now succeeded in utilizing the velocity cooling for the continuous cooling and liquefaction of gases and the separation of gas mixtures by expanding the compressed and cooled gas through an expansion valvento a space or expansion nozzle of gradually increasing sectional area so proportioned that the expansion takes place substantiallv adiabatically. By the use of suitably con structcd and proportioned expansion nozzles into which the gases are't-hus expanded, the loss of energy of the existing systems is avoided or minimized. These nozzles have a gradually increasing cross-sectional area, and may be of the type evolved by Laval. the smallest and the largest cross sections of these nozzles n-esenting such differences, and the increase from the oneto the other being so proportioned that the expanded gas in the nozzle chamber itself may fall below the pressure of the atmosphere. In such nozzles the expansion of the gas approximates adiabatic expansion, and except for slight losses by conduction may be considered as substantially zuliabatic. The process of the present invention may accordingly be considered as an adiabatic or substantially adiabatic expansion through an expansion nozzle into a space of gradually imrreasing sectional area whereby the velocity cooling may be utilized and this velocity energv made to assist in the cooling and liquefaction.

In the accompanying drawings are shown certain forms of apparatus in which the to the compressed gas; Figs. 3' and t represent similar views of another form of the apparatus with an enlarged inlet space, a part of Fig. 4 being broken off for convenience in illustration. v

In the apparatus illustrated the prelimiper square cm. and the admission aperture A of the nozzle C as 1 square mm. the velocity increases in correspondence with the diminishing pressure in the nozzle. The molecules then separate more and more from each other and when the width of the opening of the nozzle has reached 40 mm. that is to say presents a ratio to the admission aperture of 1 to 1250, the pressure of the gas has fallen to 800 grams per square cm., that is to say to a minus pressure of some what more than one-fifth of an atmosphere. It is therefore important that the lower aperture as compared with the upper aperture of the nozzle should have a substantially larger cross section. The increase in.

cross section may be so large that starting at any desired initial pressure the gas is able to expand to atmospheric pressure and below. When applying a nozzle of this construction there is a minus pressure in the gas itself which accelerates its liquefaction. By the conversion of the gas pressure into the extremely high velocities obtained by nozzle expansion a larger expenditure of external work is required so that the corresponding heat equivalent disappears and as the process takes place almost adiabatically this is only at the cost of the temperature of. a part of the expanded gas.

Rankine has already shown that the adiabatic expansionof superheated steani causes its condensation and in the Laval nozzle a highly heated liquid is converted by cooling into a mixture of liquid and vapor. The present invention is based on similar physical principles. In the first place the specific heat of the expanded gas and the partitions is consumed to cover the expendi ture of heat, then as soon as the pressure falls below atmospheric pressure a part of the gas must yield up its latent heat, that is to say it liquefies, but at first these liquid particles retain the velocities of the former gas molecules exactly like the steam condensate of a steam generator feed injector. It is an advantage of the system that this reduction of pressure below atmospheric pressure takes place merely by an increase of the velocity of the molecules without the necessity for special air pumps. Thus it is possible to cause the nozzles to open into a collecting nozzle E (Fig. 2) or a collecting tube and to convert the velocity into pressure without risk of the liquid obtained again vaporizing.

It is of course necessary by suitably forming the nozzle to prevent any friction of the gas at the nozzle walls when the gas passing therethrough is under hlgh pressures. For this purpose the portion of the nozzle near its inlet end is enlarged, as diagrammatically shown in Figs. 3 and 4. At the inlet of the gas the expansion reservoir is enlarged to a cylindrical space G so that the jet of the gas issuing from the valve B or the like does not touch the walls. In

consequence of injector action or suction a.

vacuum is formed at the outer ends H of the enlarged space G, which assists the cooling action. A purely adiabatic expansion is not possible because the metallic nozzle and the supply pipe conduct their heatto the expanded gas. In order to avoid this defect the cold imparted to the expansion valve B is transferred by a device shown in Fig. 2 directly to the compressed gas before the expansion and not only cools it, but its. property of being a poor conductor of heat is utilized for surrounding the expansion nozzle with a gas envelop which is a poor conductor. With this object the nozzle C is made of a substance which is a good conductor such as copper, and inserted in a vessel D which receives the cooled compressed gas from the inlet (A). From the vessel D the cooled compressed as is conducted to the expansion valve B, rom which it is expanded into the conical nozzle C. This apparatus can be similarly utilized for separating any foreign gases with a high boiling point from the compressed gas to be liquefied before it can exert any harmful eflect by stopping the valve. The cooling which takes place during the expansion process in the copper nozzle is consequently transferred directly to the compressed gas before its expansion and gradually cools it sufficiently to cause the foreign substances of higher boiling point as for instance water-vapor, carbonic acid, etc., contained in the compressed gas to be precipitated as liquid or solid bodies which can be drawn ofl" through a special pipe F in the bottom of the vessel D.

It will be seen that in the process of the present invention the cold compressed gas is expanded through the expansion valve into anozzle of gradually increasing sectional area, the velocity of the expanded and partly liquefied gas being made use of to assist the cooling, and being so 'made use of that the pressure falls below atmospherie in the expansion chamber or nozzle, While a higher pressure may exist at a still greater distance from the expansion valve, as has been pointed out. When the compressed gas is subjected to the cooling effect of the expanded gas the compressed gas is itself further cooled and loss of the cooling effect minimized. The energy of the expanded gas may be considered as converted into the main cooling which causes the main liquefaction and the velocity cooling which further assists and promotes this cooling.

I claim 1. The process of liquefying compressed and cooled gases having a low boiling point which comprises expanding such. gases through an expansion valve without abrupt changes in direction and then causing the gas stream to assume a gradually increasing cross-sectional area of such proportions that velocity cooling of the expanded gas is effected.

2. The process of liquefying compressed and cooled gases having a low boiling point which comprises expanding such gases through an expansion valve into a chamber having a gradually increasing sectional area and so proportionedthat velocity cooling of the expanded gas is effected, and bring ing the compressed gas before expansion into heat-interchanging relation with said chamber.

3. The rocess of 'liquefying compressed and cooled gases having a low boiling point which comprises expanding such gases from a highly compressed and cooled conditionthrough an expansion valve and causing the gas stream to assume a graduall increasing sectional area so proportione that the expanding gases by their velocity reach a lower pressure than that of the dischar e'receptacle, whereby velocity cooling 0 the gases is eflected.

In testimony whereof I have hereunto set my hand in the presence of two subscribing witnesses.

GOTTHOLD HILDEBRANDT.

Witnesses:

WOLDEMAR HAUPT, HENRY HASPER. 

